GFAP and multiple sclerosis: References for this narrative review were identified through searches of PubMed with the search terms “adult-onset multiple sclerosis”, “chronic active lesions”, “confirmed disability accrual”, “fluid biomarkers”, “grey matter”, “glial fibrillary acidic protein”, “MRI”, “neurofilaments”, “paediatric-onset multiple sclerosis”, “progression independent of relapse activity”, “repair”, “smouldering disease”, “spinal cord”, “thalamus”, “treatment”, “white matter” from 1990 until April, 2025.